A typical electrostatographic printing process includes a development step whereby developing material including toner or marking particles is physically transported into the vicinity of a latent image bearing imaging member, with the toner or marking particles being caused to migrate via electrical attraction of toner or marking particles to the image areas of the latent image so as to selectively adhere to the imaging member in an image-wise configuration. Various methods of developing a latent image have been described in the art of electrophotographic printing and copying systems. Of particular interest with respect to the present invention is the concept of forming a thin layer of liquid developing material on a first surface, wherein the layer has a high concentration of charged marking particles. The layer is brought into contact with an electrostatic latent image on another surface, wherein development of the latent image occurs upon separation of the first and second surfaces, as a function of the electric field strength generated by the latent image. In this process, toner particle migration or electrophoresis is replaced by direct surface-to-surface transfer of a toner layer induced by image-wise fields.
For the purposes of the present description, the concept of latent image development via direct surface-to-surface transfer of a toner layer via image-wise fields will be identified generally as contact electrostatic printing (CEP). Exemplary patents which may describe certain general aspects of contact electrostatic printing, as well as specific apparatus therefor, may be found in U.S. Pat. Nos. 4,504,138; 5,436,706; 5,596,396; 5,610,694; and 5,619,313.
Landa et al., in U.S. Pat. No. 5,436,706, disclose a multicolor system wherein a plurality of developer rollers are said to be provided, one for each color, which are sequentially engaged with a photoconductive surface to develop sequentially produced latent images.
Domoto et al., in U.S. Pat. No. 5,619,313, disclose a multicolor embodiment of a liquid electrophotographic simultaneous development and transfer apparatus that includes a continuous transfer belt. Four latent imaging units are positioned about the periphery of the transfer belt. Each latent imaging unit are said to be substantially identical to one another, except for the color of the liquid developer material employed therein.